The isothermal and non-isothermal crystallization kinetics of isotactic polypropylene (iPP) and iPP nucleated with the nucleating agent sodium 2,2'-methylene-bis(4,6-di-tertbutylphenyl)-phosphate (NA11), zeolite 13X (Z13X), and both NAll and Z13X were investigated. First, isothermal crystallization analyses show that the iPP/NA11/Z13X system provided the smallest half-crystallization time compared with the other three iPP systems even though a smaller amount of NAll was added in the iPP/NA11/Z13X system (0.08 wt%) relative to that of the iPP/NA11 system (0.2 wt%). Moreover, the fold surface energy of the iPP/NA11/Z13X system was also the least among all samples considered. Then, during non-isothermal crystallization, the iPP/NA11/Z13X system demonstrated the smallest value of F(T), indicating that the required cooling rate to attain a specified relative crystallinity for the system was the lowest among all systems considered. Furthermore, a comparison of the crystallization activation energy shows that the NAll and NA11/Z13X additives primarily improved the crystallization of iPP through an acceleration of the nucleation process. Finally, polarized optical microscopy results show that the NA11 and Z13X additives affected only the crystallization kinetics of iPP, and did not affect the crystallization morphology.